Semiconductor memory including reduced capacitive coupling between adjacent bit lines

ABSTRACT

A semiconductor memory apparatus comprises a plurality of complementary bit line pairs for accessing memory cells. Each of the memory cells is accessed by two complementary bit line pairs. Each of the complementary bit line pairs is connected to a corresponding sense amp circuit for amplifying a signal level difference between bit lines of a corresponding bit line pair. A plurality of sealed lines, each being connected to ground and being positioned between two adjacent bit lines of different complementary bit line pairs, are provided to avoid the formation of a line-to-line capacitance between the two adjacent bit lines.

FIELD OF THE INVENTION

The invention relates to a semiconductor memory apparatus, and more particularly to a semiconductor memory apparatus having complementary bit lines, each connected to a sense amp circuit.

BACKGROUND OF THE INVENTION

A conventional semiconductor memory apparatus of a complementary bit line type comprises a predetermined number of memory cells to provide a desired memory capacity, a predetermined number of complementary bit line pairs, among which each two complementary bit line pairs are connected to a corresponding memory cell to provide dual ports, a predetermined number of word lines, two of which word lines are connected to a corresponding memory cell to allow asynchronous access for the dual ports, and a predetermined number of sense amplifier (defined "amp" hereinafter) circuits each connected to one of the complementary bit line pairs.

In operation, it is assumed that each of the complementary bit line pairs is under "high" at first in accordance with the initialization of the memory apparatus. When a word selection signal becomes "high" on a word line for a first selected port, a signal level difference begins to be produced between bit lines of a complementary bit line pair for the first selected port dependent on a content of a memory cell. Subsequently, when a word signal becomes "high" on a word line for a second selected port, a signal level difference begins to be produced between bit lines of a complementary bit line pair for the second selected port dependent on the content of the memory cell in the same manner as in the first selected port. At this moment, a sense amp circuit connected to the bit lines for the first selected port is enabled to amplify and stabilize the signal level difference. Thus, information is read from a port corresponding to a selected memory cell. The structure and operation of the conventional semiconductor memory apparatus of the complementary bit line type will be explained in more detail later.

According to the conventional semiconductor memory apparatus, however, there are disadvantages that an erasure or a destruction of information occurs in a memory cell, and that erroneous information is read from a memory cell, because a signal level is pulled, for instance, from "high" to "low" on a bit line of the second selected port under the influence of a signal level on a bit line of the first selected port, where the bit lines of the first and second selected ports are heavily coupled by a line-to-line capacitance produced therebetween. This results in an inversion of a readout information at the second selected port.

These disadvantages will be overcome, if the line-to-line capacitance is lowered to a predetermined level between adjacent bit lines of the dual ports, or if accesses are synchronized between the dual ports. For this purpose, the length of bit lines must be shortened to reduce the line-to-line capacitance, making it difficult to increase the memory capacity. Further, access control of the dual ports will be complicated.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a semiconductor memory apparatus in which a memory capacity can be increased without the influence of a line-to-line capacitance.

It is a further object of the invention to provide a semiconductor memory apparatus in which there is no limitation in an access to dual ports.

According to the invention, a semiconductor memory apparatus comprises,

a predetermined number of memory cells, each storing a binary information;

a plurality of complementary bit line pairs, to which corresponding memory cells are connected, each complementary bit line pair being accessible to the corresponding memory cells;

a plurality of sense amplifier circuits, each connected to a complementary bit line pair and amplifying a signal level difference between bit lines of the complementary bit line pair; and

a plurality of grounded lines each provided between adjacent complementary bit line pairs and avoiding the formation of a line-to-line capacitance between adjacent bit lines of the adjacent complementary bit line pairs.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be explained in more detail in conjunction with appended drawings wherein,

FIG. 1 is a circuit diagram showing a conventional semiconductor memory apparatus,

FIG. 2 is a timing chart showing operation in the conventional semiconductor memory apparatus,

FIG. 3 is a matrix diagram showing an embodiment according to the invention,

FIG. 4 is a circuit diagram showing a pertinent portion in the embodiment of the present invention shown in FIG. 3, and

FIG. 5 is a timing chart showing operation in the embodiment at the present invention shown in FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS

Before explaining an embodiment according to the invention, the aforementioned conventional semiconductor memory apparatus of a complementary bit line type will be explained with reference to FIG. 1. The semiconductor memory apparatus comprises complementary bit line pairs D₁ and D₁, D₂ and D₂, - - - for ports 1₁, 1₂, - - - , word lines 11₁ and 12₁, - - - crossing the bit line pairs, memory cells 3, - - - to be addressed by the bit line pairs and the word lines, and sense amp circuits 4₁, 4₂, - - - each connected to a corresponding bit line pair among the bit line pairs. One of the memory cells 3 includes transfer gate MOS transistors 3A, 3B, 3C and 3D, and driver MOS transistors 3E and 3F. As clearly shown in FIG. 1, the transfer gate transistors 3A and 3B are connected to the bit line pair D₁ and D₁ and the word line 11₁, and the transfer gate transistors 3C and 3D are connected to the bit line pair D₂ and D₂ and the word line 12₁. On the other hand, the driver transistors 3E and 3F are connected by drain electrodes thereof through the transfer gate transistors 3A, 3B, 3C and 3D to the bit line pairs and the word lines, and by source electrodes to the ground. If it is assumed that a content of the memory cell 3 is "1", the drain electrode of the driver transistor 3E is "high", so that the driver transistor 3F is connected to ground rendered conductive. Therefore, (coupled to ground) the drain electrode of the driver transistor 3F is "low", so that the driver transistor 3E is not connected to ground rendered conductive.

The sense amp circuits 4₁ and 4₂ include MOS transistors 4A₁, 4B₁ and 4C₁, and 4A₂, 4B₂, and 4C₂, and allow a sense amp enabling signal to be applied to each of the gate electrodes of the MOS transistors 4C₁ and 4C₂. In this semiconductor memory apparatus, parasitic capacitances C₁, C₃, C₄, C₅, C₆ and C₇ are produced as shown in FIG. 1, and a line-to-line capacitance C₂ is produced between the bit lines D₁ and D₂.

In operation, the bit lines D₁, and D₁, and D₂ and D₂ for the ports 1₁ and 1₂ are initialized to be "high" at first as shown in FIG. 2. At time t₁, when a word selection signal for the port 1₁ is enabled on the word line 11₁, a signal level difference begins to be produced between the bit lines D₁ and D₁ for the port 1₁ in accordance with a content "1" of the memory cell 3 as described before. Subsequently, when a word selection signal for the port 1₂ is enabled on the word line 12₁ at time t₂, a signal level difference begins to be produced in the same manner as in the port 1₁. At this moment, an enabling signal is applied to an enabling signal line 6₁ of the MOS transistor 4C₁ in the sense amp circuit 4₁, so that the signal level difference between the bit lines D₁ and D₁ for the port 1₁ is amplified in the sense amp circuit 4₁ to stabilize a state of the signal level difference. In this situation, a signal level of the bit line D₂ for the port 1₂ is pulled from "high" to "low" in accordance with the influence of the line-to-line capacitance C₂ as indicated by a point P₁, although the signal level is inherently "high" dependent on the content of the memory cell 3. On the contrary, a signal level of the bit line D₂ becomes "high" invertedly. At time t₃, a sense amp enabling signal is applied to an enabling signal line 6₂ of the MOS transistor 4C₂ in the sense amp circuit 4₂ to read information from the memory cell 3 at the port 1₂. Although the signal level of the bit line D₂ exhibits a tendency to restore the inherent state as indicated by a point P₂, it can not get back to a state correctly based on the content of the memory cell 3. As a result, an inverted signal is read at the port 1₂ from the memory cells. Therefore, the aforementioned disadvantages are produced by the conventional semiconductor memory apparatus of the complementary bit line type.

Next, a semiconductor memory apparatus of a complementary bit line type while referring to an embodiment according to the invention will be explained in FIG. 3. The semiconductor memory apparatus comprises memory cell arrays 2₁, 2₂, 2₃, - - - , each of which includes memory cells 3₁, 3₂, 3₃, - - - each connected to bit line pairs D₁ and D₁ for a port 1₁, D₂ and D₂ for a port 1₂, - - - and to corresponding word lines 11₁ and 12₁, 11₂ and 12₂, 11₃ and 12₃, - - - , sense amp circuits 4₁, 4₂, 4₃, 4₄, 4₅, 4₆ - - - each connected to a corresponding bit line pair among the bit line pairs D₁ and D₁ for the port 1₁, and D₂ and D₂ for the port 1₂, and other bit line pairs for ports 1₃, 1₄, 1₅, 1₆ - - - , and to sense amp enabling line 6₁ or 6₂, and sealed lines 5₁, 5₂, 5₃, 5₄, 5₅, - - - each connected to ground and provided between bit lines for each two adjacent ports.

FIG. 4 shows a pertinent portion of the semiconductor memory apparatus in the embodiment of FIG. 3, wherein like parts are indicated by like reference numerals in FIGS. 1 and 3. The difference between the semiconductor memory apparatus in the embodiment and the conventional one is that the former further comprises the sealed (grounded) lines 5₁, 5₂, 5₃, 5₄, 5₅, - - - to avoid the aforementioned influence of the line-to-line capacitance. As shown in FIG. 4, the line-to-line capacitance C₂ is no longer produced when the grounded line 5₂ is provided between the bit lines D₁ and D₂. Instead, capacitances C₂₁ and C₂₂ are produced between the bit line D₁ and the grounded line 5₂, and the grounded line 5₂ and the bit line D₂. The grounded line 5₂ is preferably provided, such that the capacitances C₂₁ and C₂₂ are equal in value.

In operation, the bit lines D₁ and D₁, and D₂ and D₂ for the ports 1₁ and 1₂ are initialized to be "high" at first as shown in FIG. 5. At time t₁, when a word selection signal for the port 1₁ is enabled on the word line 11₁, a signal level difference begins to be produced between the bit lines D₁ and D₁ for the port 1₁ in accordance with a content "1" of the memory cell 3 in the same manner as in the conventional memory apparatus. Subsequently, when a word selection signal for the port 1₂ is enabled on the word line 12₁ at time t₂, a signal level difference begins to be produced in the same manner as in the port 1₁. At this moment, an enabling signal is applied to an enabling signal line 6₁ of the MOS transistor 4C₁ in the sense amp circuit 4₁, so that the signal level difference between the bit lines D₁ and D₁ for the port 1₁ is amplified in the sense amp circuit 4₁ to stabilize a state of the signal level difference. At the same time, a signal level difference begins to be produced between the bit lines D₂ and D₂ for the port 1₂ in accordance with the content of the memory cell 3. In this situation, a signal level of the bit line D₂ continues to be "high", because there is no line-to-line capacitance between the bit lines D₁ and D₂. At time t₃, an enabling signal is applied to an enabling signal line 6₂ of the MOS transistor 4C₂ in the sense amp circuit 4₂, so that the signal level difference between the bit lines D₂ and D₂ for the port 1₂ is amplified in the sense amp circuit 4₂ to stabilize a state of the signal level difference. Thus, information of the memory cell 3 can be read at the dual ports 1₁ and 1₂ without any complicated control in regard to a read-out timing and so on.

Although the invention has been described with respect to specific embodiment for complete and clear disclosure, the appended claims are not to thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth. 

What is claimed is;
 1. A semiconductor apparatus, comprising:a predetermined number of memory cells, each storing a binary information; a plurality of complementary bit line paris, wherein two of said complementary bit line pairs are coupled to a corresponding memory cell of said memory cells, and wherein two of said complementary bit line pairs are accessible to each of said corresponding memory cell; a plurality of sense amplifier circuits, each of said sense amplifier circuits being connected to a corresponding one of said complementary bit line pairs for amplifying a signal level difference between bit lines of said corresponding complementary bit line pair; and a plurality of grounded lines, each of said grounded lines having a fixed potential and being provided between adjacent ones of said complementary bit line pairs so as to avoid the formation of a line-to-line capacitance which is normally produced between two adjacent bit lines of different adjacent complementary bit line pairs.
 2. A semiconductor memory apparatus according to claim 1, wherein at least one of said grounded lines is disposed so as to respectively provide an equal capacitance value between two adjacent bit lines of different complementary bit line pairs and said at least one of said grounded lines. 